Rigid plastic frames

ABSTRACT

A method for the production of frames from rigid plastic profiles for use on refrigerator cabinets and in particular on chest freezers, which comprises forming the plastic profiles, mitering and welding the edges of the plastic profiles to form a frame having sharp-edged corners, and rounding at least one of the sharp-edged corners by means of thermo-forming. 
     The invention also comprises the finished frame thereby obtained and its application in the field of refrigerator cabinets and in particular, chest freezers.

CROSS-REFERENCE

This is a division of my copending application Ser. No. 822,463, filedJan. 27, 1986, now U.S. Pat. No. 4,718,960, issued Jan. 12, 1988.

The present invention relates to the production of plastic frames forcabinets, and particularly to frames for refrigerator or freezercabinets.

Frames for cabinets, such as refrigerator or freezer cabinets, havepreviously been prepared by welding metal or plastic profiles to formthe frame. In particular, extruded segments of rigid plastic profileshave been welded end-to-end to form frames for refrigerator or freezercabinets. These prior art plastic profiles have the disadvantage,however, of leaving the finished frame with sharp and hence unsafecorners.

Frames with sharp corners also present problems in the manufacture ofrefrigerators and freezers, particularly chest freezers that open fromthe top. It is known that chest freezers have walls made of parallelinternal and external wall parts that define a cavity into which thecooling ducts or tubing are placed. However, the cooling ducts or tubingmust be placed as closely as possible to the internal wall parts toobtain the highest thermal efficiency, but it is difficult to do so atthe corners, because the curved ducts or tubing will be widely spacedfrom the internal wall at each corner. This results in a loss of thermalefficiency at the corners.

A frame having sharp corners also presents problems when it is desiredto use an internal wall furnished with a "roll-bond", which as is known,is obtained from two sheets of aluminum adhesively attached together.The "roll-bond" is furnished on all four reaches of the internal walland must have a curved radius such that the channels for the coolingliquid are not closed off inside the "roll-bond". The presence of sharpcorners would thus interfere with the "roll-bond".

The present invention now provides a method for the production of frameshaving rounded corners from rigid plastic profiles for use inrefrigerator cabinets and in particular chest freezers, which comprisesthe steps of forming the plastic profiles, mitering and welding the endsof the plastic profiles to form a frame having sharp-edged corners, androunding at least one of the sharp-edged corners by means ofthermo-forming. The present invention also provides the finished framethereby obtained.

The present invention is illustrated in terms of the accompanyingdrawings, in which:

FIG. 1 is a plan view of a portion of a frame having sharp-edgedcorners, with the thermo-forming equipment in its starting position;

FIG. 2 is a view in section taken along lines II--II of FIG. 1;

FIG. 3 is a view similar to FIG. 1, showing the first thermo-formingstage;

FIG. 4 is a view of section taken along lines IV--IV of FIG. 3;

FIG. 5 is a view similar to FIG. 1 showing the final thermo-formingstage;

FIG. 6 is a view in section taken along lines VI--VI of FIG. 5;

FIG. 7 is a perspective view, partly in section of the frame of theinvention assembled on a chest freezer; and

FIG. 8 is a detail view, in section, of a portion of the frame shown inFIG. 7.

Referring to FIG. 1, frame 10 is comprised of four extruded, rigidplastic profile segments 11, which have been mitered to form edges 12that are heat-welded together to form four 90° sharp corners, one ofwhich being shown in FIG. 1. The production of the profiles 11 and themitering and welding operations are well known in the art.

The cross-section of frame 10 is substantially saw-shaped and comprisesside parts 13 and 14, which delimit frame 10, internally and externally,and vertical ribs 15 and 16. The junctions of edges 12 of each pair oflengths of profiles 11 thus provide a sharp-edged outer corner 17corresponding to the welding of a pair of parts 13, and a sharp-edgedinner corner 18 corresponding to the welding of a pair of parts 14.

Each corner 17, 18 of frame 10 is positioned as shown in FIGS. 1 and 2relative to a thermo-forming unit comprising a countermold 19, whichacts as a fixed support for the frame 10, and a mold comprising severalforming tools, for example three forming members 20, 21, and 22 eachcomprising a piston 23, 24, and 25, respectively, connected to acylinder 26, 27 and 28, respectively. Each piston 23, 24, 25 isfurnished with a head substantially complementary to the shape of thepart of the frame 10 with which said head will move into contact, withthe exceptions later described hereunder. In particular, the piston 23is furnished with a substantially asymetric T-shaped head 29.

FIGS. 1 and 2 show the molds in their starting position. The head of thepiston 23 is inserted under the corner 17 of the frame 10 between thevertical rib 16 and the external part 14. The surface 30 of the head 29,which is in contact with the inner corner 18 of the frame 10, has acurved configuration that is complementary to the configuration of thesurface 31 of head 32 of piston 24. The surfaces 30 and 31, relative tothe inner corner 18, have a concave and a convex configuration,respectively. The thermo-forming unit is furnished with suitableelements (not shown) for heating the frame, which can be located in thecountermold 19 or the mold or both. The heating elements can beradiation heating elements or other suitable heaters.

The thermo-forming operation proceeds from the starting position asshown in FIGS. 1 and 2 to the first stage schematically shown in FIGS. 3and 4 whereby, while the forming members 20 and 22 remain in theirstarting position, the piston 24 of forming member 21 moves into contactwith the corner 18 of the frame 10 facing said members. The piston 24reaches its stroke-limit while maintaining an air space 35 (FIG. 4)between the piston head and frame 10. FIGS. 5 and 6 show the final stageof the thermo-forming operation, whereby the forming members 22 and 20,with their respective pistons 25 and 23, move into contact with thecorresponding parts of the frame 10 facing said members. In particular,the head 29 of the piston 23 pushes corner 18 against the surface 31 ofthe head of the piston 34, said corner being thermo-formable due to theheat applied. Owing to the complementary concave and convexconfiguration of the surfaces 30 and 31, respectively, the corner 18assumes the corresponding rounded final configuration shown in FIGS. 6and 7, with the air space 35 consequently being filled. At the sametime, by means of the pushing action of piston 25, the outer corner 17of frame 10 is rounded against the curved configuration of the surface34 of head 33 of piston 25.

FIG. 7 shows the final configuration of the finished frame 10 in whichthe corners 17 and 18 are rounded. Frame 10 thus obtained may beassembled on a chest freezer with metallic external wall 36 and internalwall 37. The cavity thereby obtained is filled with an insulatingmaterial 38 surrounding the coiled ducts 39 containing cooling fluid,the ducts being in parallel relationship to and adjacent the internalwall 37. As clearly seen in FIG. 8, the internal wall 37 is fittedbetween the vertical rib 16 and the part 14 of the frame 10 and canfollow the curved configuration of the frame, thereby enabling thecoiled cooling ducts on the tubing 39 containing the copling liquid orthe "roll-bond" (not shown) to be as close as possible to the internalwall 37 of the freezer chamber, thus improving the thermal performanceof said freezer.

Another important advantage of the present invention is that thefinished frame 10 thereby obtained has no sharp-edged corners, therebyavoiding the dangers such corners present.

I claim:
 1. A frame for use in refrigerator and freezer cabinets andparticularly chest freezers, which comprises four mitered rigid plasticprofiles welded together at their ends to form a frame having weldedinner and outer 90° corners, said frame, when disposed in a horizontalposition, having an upper base portion with an outer edge and an inneredge, a side wall depending from said inner edge and providing an innerwall of said frame, said inner wall being rounded to provide at leastone rounded inner corner and a rib depending from said base adjacent tobut spaced apart from said inner wall.
 2. The frame according to claim1, wherein said inner wall is round at each of said inner corners toprovide four rounded inner corners.
 3. A frame for use in refrigeratorand freezer cabinets and particularly chest freezers, which comprisesfour mitered rigid plastic profiles welded together at their ends toform a frame having welded inner and outer 90° corners, said frame, whendisposed in a horizontal position, having an upper base portion with anouter edge and an inner edge, a said wall depending from said inner edgeand providing an inner wall of said frame, said inner wall being roundedto provide at least one rounded inner corner, a rib depending from saidbase adjacent to but spaced apart from said inner wall and an outer walldepending from said outer edge.